Keep in mind when planting that Bettina Rothschild is thought of as tender, so remember to wait until your soil is warm and the night time temperature is well above freezing before moving outside.
By our calculations, you should look at sowing Bettina Rothschild about 91 days before your last frost date.
Ensure that temperatures are mild and all chance of frost has passed before planting out, as Bettina Rothschild is a tender plant.